The presently disclosed embodiments relate to ink jet architectures for high speed production printing, and more particularly, production piezo ink jet (PIJ) architectures employing a large array of printheads in a direct to web architecture; however, the embodiments also apply to other modular jet architectures producing print by employing a large array of printheads.
A piezo ink jet printhead will expel a volume of ink upon an ink chamber contraction resulting from an applied voltage. Normally the ink has to be heated to a comparatively high temperature because the ink will be solid at room temperature. In a production printing embodiment, 20 or more printheads are configured in an array with each printhead having several hundred jets. Because all jets must be working at the same time, reliability requirements for the printheads are compounded. In other words, the need to mitigate disruptions associated with jet failures is critically important in any production printing embodiment that employs large numbers of non-redundant jets.
Printheads experience a jet failure whenever any of their jets are either not jetting enough ink or not jetting any ink at all. Some jet failures are intermittent, which means the corresponding jets either spontaneously recover, or are recovered by a maintenance procedure. Other jet failures are chronic, which means the function of the corresponding jets cannot be recovered. When a jet fails, it is not known if the failure is chronic until several attempts to recover the jet have failed.
The process of attempting to recover failed jets is fairly involved and not always successful. First, a relatively large volume of ink is forced through the head in an effort to purge whatever is blocking the failing jet. The nozzle plate is then wiped and the printhead jetting performance is inspected. The purge, wipe and inspect cycle is repeated until either jet performance is restored or until the service operator considers one or more jet failures to be unrecoverable. With such a large total number of jets, stopping a large production web for every jet shortfall is untenable. Even assuming rates of hard or chronic jet failures are manageable, soft or recoverable printhead failures still have the potential of being very disruptive.
One can imagine that for a large roll of paper comprising a production web, if a purging operation had to occur every time any one of the substantial number of jets failed, then the purge operation would be very disruptive to the extent that no reasonable commercial operation could result. Nevertheless, jet failures have to be dealt with, and in a typical production environment, operators may frequently be faced with an uncomfortable trade-off between printing with less than optimal jet performance versus dealing with the potentially time consuming disruption of performing printhead purge and maintenance cycles, and the additional trouble shooting procedures in the printer to recover one or more printheads. When a failing printhead has to be “swapped” with a replacement head, a “cold swap” is performed so that the system cannot return to a production ready state until the replacement unit and the delivery ink are heated to a print-ready production status and the function of the new head is verified.
The problem sought to be overcome by the subject embodiments is undesirable down time of system functioning due to faulty printheads. A solution would minimize the down time and repair recoverable faulty printheads. More particularly, there is a need for a print system printhead recovery unit to rejuvenate printheads and determine whether or not a head failure is chronic or recoverable so that an operator can assess proper further handling of the faulty printhead while the printing system continues to operate in production mode.